1. Field of the Invention
The invention relates to a hub unit bearing for a driving wheel of an automobile, and more particularly to a unified bearing including an axle hub, an outer joint member of constant velocity universal joint and an axle bearing.
2. Prior Art
Power transmission system for transmitting the power from an automotive engine to driving wheels is required to cope flexibly with angular displacement and axial displacement caused by changes in relative positional relation between the engine and the wheels, and therefore, as shown in FIG. 9, for example, a driving shaft 1 is interposed between the engine and a driving wheel. One end of the driving shaft 1 is coupled to the differential gear through a sliding type constant velocity universal joint J1, while the other end is coupled to a driving wheel 2 through a fixed type constant velocity universal joint J2. Plunging of the sliding type constant velocity universal joint J1 absorbs the axial displacement. The fixed type constant velocity universal joint J2 can absorb only the angular displacement.
The fixed type constant velocity universal joint J2 is mainly composed of an inner joint member 4 fitted to the other end of the driving shaft 1, an outer joint member 3 coupled to an axle hub 7, plural balls 5 for transmission of torque interposed between pairs of ball grooves of the inner joint member 4 and outer joint members 3 and 4, and a retainer or cage 6 interposed between an outer spherical surface of the inner joint member 4 and an inner spherical surface of the outer joint member 3 for retaining the balls 5. The axle hub 7, carrying a wheel disc of the driving wheel 2, is rotatably supported by an axle bearing 8.
The axle hub 7, outer joint member 3 of constant velocity universal joint J2 and axle bearing 8 are assembled into a unit to compose a hub unit bearing H.
The axle bearing 8, which is a double row rolling bearing, is fixed to the car body through a knuckle joint 9, one 8a of the double rows of balls 8a and 8b lying outboard, and the other 8b inboard of the vehicle. The inboard ball row is subjected to hat from the outer joint member 3 of the constant velocity universal joint J2 receiving torque from the driving shaft 1, which in combination with poor heat radiating capability of the inboard side, requires very strict load conditions.
Since the axle hub 7 is coupled to the constant velocity universal joint J2 by means of bolts and others and is supported on the axle bearing 8, it is also subjected to and thermal effects from the constant velocity universal joint J2 and axle bearing 8. Thus, in the axle hub 7, a favorable cooling state is hardly obtained, and therefore the life of the hub unit bearing H is shortened by adverse thermal effects.
It is hence an object of the invention to increase the rigidity of the hub unit bearing to improve its durability, and also to realize a small-size and a compact design thereof.
It is another object of the invention to provide a hub unit bearing with an improved structure of the axle hub having an excellent cooling efficiency.